Portable equipment is often provided operative power from power packs constructed of primary batteries or secondary batteries. If the equipment is in a location with fixed power available, the equipment may be provided operative power by an external power source. Simultaneously with providing operative power from the external power source it is also desirable to charge the secondary batteries, if they are disposed in the power pack. If primary batteries are disposed in the power pack the external power source must not attempt to charge these batteries. This is because primary batteries can be irreversibly damaged and in some cases may explode, if there is an attempt to charge these primary batteries.
Prior solutions to this problem have either warned the user not to install primary batteries when external power is connected, or used mechanically interlocked power receptacles. These mechanically interlocked power receptacles connect the external power to the load while disconnecting the battery power from the load. The problem with this approach is that the disconnect mechanism is subject to physical wear and further is very difficult to seal. Without an adequate seal the electrical circuitry internal to the portable equipment can be damaged. Further, with this approach, if secondary batteries are installed they will not be charged simultaneously with the external power source providing operative power.
What is needed is an improved portable equipment power supply with provision for externally provided power to provide operative power while charging a secondary battery power pack but preventing the charging of a primary battery power pack.